Antigen presentation to HLA class II-restricted measles virus-specific T-cell clones can occur in the absence of the invariant chain

A human fibroblast line expressing HLA-DR1 antigen on its surface was generated by transfection with DRα and DRβ cDNAs. Expression of the invariant chain gene was not detectable in the transfected fibroblasts and was not induced by infection with measles virus. Lysis of measles virus-infected cells occurred with DR1- but not with DR4-restricted measles virus-specific cytotoxic T-lymphocyte (CTL) clones and was inhibited by a monoclonal antibody specific for DR antigen. Therefore, the invariant chain is not required for DR-restricted presentation of measles virus antigens by this fibroblast line. Transfected fibroblasts were lysed as efficiently as an autologous B-cell line even though they expressed much less surface DR antigen. Lysis of both the transfected fibroblasts and the B-cell line was insensitive to treatment with chloroquine. These results demonstrate that expression of a DR αβ heterodimer at the surface of this fibroblast line is necessary and sufficient for presentation of measles virus antigens to specific CTL clones.